Giant cystic hypothalamic hamartoma in an infant associated with persistent syndrome of inappropriate antidiuretic hormone secretion

Background: A giant hypothalamic hamartoma (GHH) is a rare congenital malformation only reported in a few cases in the literature and is often associated with precocious puberty, gelastic seizures, or less commonly, Pallister-Hall syndrome. Persistent syndrome of inappropriate antidiuretic hormone secretion (SIADH) is very rare in infancy, and most patients with GHH do not develop persistent SIADH, usually only transient electrolyte disturbances postoperatively. Previous cases of GHH have not been associated with persistent derangements in antidiuretic hormone levels. Case description: A 7-month-old male infant presented to our hospital with a history of an intracranial cystic lesion diagnosed at 23 weeks gestational age (GA), later impressed as a solid-cystic mass at 37 weeks GA by ultrasound prenatally. Postnatal MRI after birth showed a large mass with a dorsal cyst occupying the hypothalamus, causing hydrocephalus and brainstem compression. The patient started to have subtle seizures on the seventh day after birth and eventually developed dacrystic seizures. Hyponatremia with persistent SIADH was observed at 3 months of age before surgery. He received long-term oral sodium supplementation, polytherapy of anti-epileptic medications, ventriculocystostomy for progressive enlargement of the cystic cavity, and later surgical treatment for disconnection and partial resection which confirmed a histological diagnosis of hypothalamic hamartoma. Conclusion: In this case study, we present a novel association of GHH with persistent SIADH and a rare presentation of a cystic component at the dorsal part of the tumor. Clinicians should be aware of this potential endocrine derangement and provide emergent treatment.